Glycolysis Lecture Notes

Introduction

• Analogy for Glycolysis: Like stripping a car for parts to use elsewhere.
• Role of Glycolysis: Glucose is ingested from carbohydrates, electrons are stripped and given to mitochondria for ATP production, the body's energy currency.

Glucose Basics

• Chemical Structure: C₆H₁₂O₆
  • 6 Carbons, 12 Hydrogens, 6 Oxygens
• Focus on Carbons: Important for the glycolysis process.

Transport of Glucose into Cells

• Transporter Requirement: Glucose is too large/has a charge, needs transporters to move into liver cells.
• Types of Glucose Transporters (GLUT):
  • GLUT 1: Blood, fetus, blood-brain barrier
  • GLUT 2: Kidneys, small intestines, liver, pancreas
  • GLUT 3: Placenta, neurons, kidneys
  • GLUT 4: Muscle and fat (requires insulin)
• Mnemonic: "Big fat bullies kick small little pansies producing nervous kids and mad fathers."

Insulin and Glucose Transport

• Insulin Dependency:
  • Non-Insulin Dependent: GLUT 1, 2, 3
  • Insulin Dependent: GLUT 4 (Muscle and fat significant in body mass)

Glycolysis Steps

Initial Steps

1. Glucose to Glucose 6-Phosphate

   • Enzyme: Hexokinase (liver) / Glucokinase (elsewhere)
   • ATP Use: ATP donates a phosphate to glucose, converting it to Glucose 6-Phosphate.

2. Glucose 6-Phosphate to Fructose 6-Phosphate

   • Enzyme: Phosphohexose isomerase
   • Reversible Reaction: Rearranges glucose without adding/removing atoms.

3. Fructose 6-Phosphate to Fructose 1,6-Bisphosphate

   • Enzyme: Phosphofructokinase
   • Irreversible Reaction: ATP donates another phosphate.
   • Molecule Unstable: Allows for the splitting into two 3-carbon molecules.

Splitting of Molecules

4. Split into Glyceraldehyde 3-Phosphate and Dihydroxyacetone Phosphate
   • Enzyme: Aldolase
   • Isomerization: Triose phosphate isomerase converts dihydroxyacetone phosphate to glyceraldehyde 3-phosphate.

Energy Harvesting Stage

5. Glyceraldehyde 3-Phosphate to 1,3-Bisphosphoglycerate

   • Enzyme: Glyceraldehyde 3-phosphate dehydrogenase
   • NAD+ to NADH: First electron stripping, important for later steps.

6. 1,3-Bisphosphoglycerate to 3-Phosphoglycerate

   • ATP Production: ADP is phosphorylated to ATP.
   • Enzyme: Phosphoglycerate kinase

7. 3-Phosphoglycerate to 2-Phosphoglycerate

   • Enzyme: Phosphoglycerate mutase

8. 2-Phosphoglycerate to Phosphoenolpyruvate (PEP)

   • Enzyme: Enolase

Final Steps

9. PEP to Pyruvate
   • Enzyme: Pyruvate kinase
   • ATP Production: Another ATP is formed.

Outcome of Glycolysis

• Products:
  • 2 Pyruvate molecules
  • Net gain of 2 ATP (4 produced, 2 used)
  • 2 NADH
• Pyruvate Pathways:
  • Can be converted to lactate (anaerobic conditions)
  • Can enter the Krebs cycle as Acetyl-CoA (aerobic conditions)

Importance of Glycolysis

• Role in Energy Production: Central pathway for ATP production.
• Adaptable Under Different Conditions:
  • Produces lactate during anaerobic exercise to mop up excess hydrogen ions.

Conclusion: Glycolysis is a crucial biochemical pathway for energy production, adaptable to different physiological conditions. The process involves multiple steps of phosphorylation and isomerization to ultimately produce ATP and pyruvate, which can further contribute to energy production through other metabolic pathways.